1. Field of the Invention
The present invention relates to a projection display device for a vehicle which performs display by using light reflection on a windshield (window glass) of a vehicle.
2. Description of the Related Art
For example, a general vehicular head-up display device (hereinafter, referred to as “HUD device”) projects an image of light including various pieces of information to be displayed to a front windshield or combiner (reflection plate) in the vicinity of the front windshield, and forms an optical path so that the light reflected by the front windshield or the like is oriented in the viewpoint direction of a driver. Accordingly, while visually recognizing the scenery in front of the vehicle, the driver can visually recognize the image (hereinafter, referred to as “display image”) which is projected from the HUD device that reflects the image to the front windshield or the like as a virtual image. In other words, while maintaining a usual driving state, the driver can visually recognize the display image by the HUD device without moving a line of sight.
However, in the device which projects the display image on a surface of the windshield or the like similar to the HUD device, there is a case where distortion is generated in the virtual image which is visually recognized by the driver. For example, examples of a reason for the distortion include the fact that the driver may view the display image projected to the surface of the windshield from an oblique direction, and the fact that the surface itself of the windshield may have a shape of a smoothly curved surface. Furthermore, since a curvature at each location on the windshield or an inclination angle with respect to a horizontal surface (or perpendicular surface) varies, there are cases where various distortions are generated in the virtual image in accordance with this situation. Additionally, in a case where the display image is projected using an enlargement optical system, there is a case where distortion is generated due to the curved surface shape of a lens and a mirror included in the enlargement optical system. The distortion negatively influences visibility of the display image.
Usually, in such distortion (aberration), three-dimensional distortion of the display image (virtual image) caused by “image surface curvature” is one of the main reasons for deterioration of the visibility of the display image.
Since the distortion of the three-dimensional display image is reduced, the HUD device (hereinafter, referred to as “device in the related art”) described in PTL 1 projects the laser light emitted from a laser module onto a screen which is provided in the middle of the optical system of the HUD device and is curved in a predetermined shape, before projecting the laser light to the windshield or the like. After this, the light emitted (reflected) from the image (curved image) projected to the screen is projected to the windshield via a recessed surface mirror or the like. In this manner, the device in the related art corrects the image surface curvature of the virtual image by once forming the curved image on the curved screen.
PTL 1 is JP-A-2013-25205.
As described above, the device in the related art reduces the three-dimensional distortion of the display image (virtual image) caused by the “image surface curvature” which is generated due to the characteristics of the windshield or the like, by employing the screen having a certain shape in the middle (on the optical path) of the optical system of the HUD device.